1. Field of the Invention
The present invention relates to a wavelength conversion device composed of a semiconductor laser device and a nonlinear optical element having a planar optical waveguide, which are mounted on a substrate in an integrated manner.
2. Related Background Art
In order to realize a high-density optical disk and a high-definition display, small short-wavelength light sources generating a laser beam in a blue range through violet range are desired. Techniques for obtaining a laser beam in this wavelength range include a second harmonic-wave generation method (hereinafter referred to as xe2x80x9cSHGxe2x80x9d) that employs a wavelength conversion device using a planar optical waveguide according to a quasi-phase-matching method, by which a wavelength of a semiconductor laser can be converted from 850 nm into 425 nm.
To miniaturize a short-wavelength light source according to this method, it is effective to mount a wavelength conversion device and a semiconductor laser device on a substrate in an integrated manner.
FIG. 15 shows one example of these small short-wavelength light sources, which is a wavelength conversion device disclosed in JP 2000-284135 A.
A semiconductor laser device 306 and a planar optical waveguide device 305 are mounted on a silicon substrate 300 in an integrated manner. The planar optical waveguide device 305 functions as a wavelength conversion device structured by forming a proton exchange planar optical waveguide 304 and a diffraction grating (not illustrated) with periodic domain inverted regions formed therein on an Mg doped LiNbO3 substrate 302. In addition, on the silicon substrate 300, electrodes 307 electrically connected to the semiconductor laser device 306 are formed, and alignment keys 301 are formed at positions 10 xcexcm away from the planar optical waveguide 304. On each side of the planar optical waveguide 304, alignment keys 303 are formed using a film made of the same material (e.g., Ta) and having the same thickness as those of the alignment keys 301. Further, alignment keys 308 are formed on the semiconductor laser device 306 as well.
Here, the semiconductor laser device 306 is a Distributed Bragg Reflector (hereinafter, referred to as xe2x80x9cDBRxe2x80x9d) type semiconductor laser device. As shown in FIG. 15, the electrodes 307 are connected to each of a gain region and a wavelength control region, i.e., a DBR region (not illustrated) of the semiconductor laser device 306.
The semiconductor laser device 306 and the planar optical waveguide device 305 are mounted onto the silicon substrate 300 in such a manner that a laser beam emitted from the semiconductor laser device 306 is guided through the optical waveguide 304 in the planar optical waveguide device 305, and the alignment keys 308, 303, and 301 are arranged at their predetermined positions. In this wavelength conversion device, a center line M1-M2 of the silicon substrate 300, a center line M5-M6 of the semiconductor laser device 306, and a center line M3-M4 of the planar optical waveguide device 305 approximately coincide with one another.
In the future, to miniaturize an optical information processing system employing an optical disk and a display still more than present ones, an optical pick up unit included in an optical disk or the like needs to be made small. To this end, it becomes effective to make a wavelength conversion device smaller.
Meanwhile, when electrically driving such a wavelength conversion device, an oscillation wavelength of a laser beam emitted from the semiconductor laser device 306 needs to be controlled so as to maximize a conversion efficiency of the laser beam by the SHG.
In the wavelength conversion device shown in FIG. 15, by controlling a current applied to the electrode connected to the DBR region, among the electrodes 307, a refractive index of the DBR region is varied so as to change a Bragg wavelength, whereby the oscillation wavelength is controlled. In this wavelength conversion device, however, a phase of the emitted laser beam cannot be controlled, because the semiconductor laser device 306 consists of only two regions, i.e., the gain region and the DBR region. Due to such a constraint, if a Bragg wavelength in the DBR region is varied by the passage of the electric current, then a so-called mode hoping would occur, where the oscillation wavelength changes discontinuously. In this case, it becomes difficult to control the oscillation wavelength, which might interfere with the operation of the device significantly.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a small short-wavelength conversion device composed of a semiconductor laser device and an optical waveguide device, which are mounted on a substrate in an integrated manner.
To fulfill the above-stated object, a wavelength conversion device according to an embodiment of the present invention, which converts a wavelength by second harmonic-wave generation and generates a laser beam, includes: a substrate having a plurality of electrodes; a semiconductor laser device mounted on the substrate and electrically connected to the plurality of electrodes; and a nonlinear optical element having an optical waveguide for guiding a laser beam emitted from the semiconductor laser device and for converting a wavelength of the laser beam. Here, the nonlinear optical element is mounted on the substrate in such a manner that the optical waveguide in the nonlinear optical element is located away from the center line of the substrate.
To fulfill the above-stated object, a wavelength conversion device according to another embodiment of the present invention, which converts a wavelength by second harmonic-wave generation and generates a laser beam, includes: a substrate having a plurality of electrodes; a semiconductor laser device electrically connected to the plurality of electrodes; and a nonlinear optical element having an optical waveguide for guiding a laser beam emitted from the semiconductor laser device and for converting a wavelength of the laser beam. Here, the semiconductor laser device, the optical waveguide of the nonlinear optical element, and the plurality of electrodes are on approximately one line on the substrate.
It is another object of the present invention to provide a wavelength conversion device by which an oscillation wavelength of a laser beam emitted from a semiconductor laser device can be controlled with stability.
To fulfill the above-stated object, a wavelength conversion device according to an embodiment of the present invention, which converts a wavelength by second harmonic-wave generation and generates a laser beam, includes: a substrate having a plurality of electrodes; a semiconductor laser device mounted on the substrate and including three regions of a gain region, a phase control region, and a wavelength control region; and a nonlinear optical element mounted on the substrate and for converting a wavelength of a laser beam emitted from the semiconductor laser device. Here, the plurality of electrodes include a first electrode group formed corresponding to the three regions and a second electrode group for carrying out wire-bonding with an external power source, the three regions of the semiconductor laser device are connected electrically to the respective electrodes in the first electrode group, and the first electrode group further is connected to the respective electrodes in the second electrode group via wires, and a wire among the wires, which is connected between the phase control region and the wavelength control region of the semiconductor laser device, has a portion functioning as a resistor.